Add txgs-<pool> kstat file
Create a kstat file which contains useful statistics about the
last N txgs processed. This can be helpful when analyzing pool
performance. The new KSTAT_TYPE_TXG type was added for this
purpose and it tracks the following statistics per-txg.
txg - Unique txg number state - State (O)pen/(Q)uiescing/(S)yncing/(C)ommitted birth; - Creation time nread - Bytes read nwritten; - Bytes written reads - IOPs read writes - IOPs write open_time; - Length in nanoseconds the txg was open quiesce_time - Length in nanoseconds the txg was quiescing sync_time; - Length in nanoseconds the txg was syncing
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>